Ac Conductivity Studies Research Articles

Dielectric and AC-conductivity studies of Dy2O3 doped (K0.5Na0.5)NbO3 ceramics

(K0.5Na0.5)NbO3 + x wt.% Dy2O3 (x = 0–1.5) ferroelectric ceramics were prepared by conventional solid state reaction method. XRD patterns revealed that orthorhombic symmetry has transformed into psuedocubic symmetry with increasing the substitution of Dy3+ in the Na+ site. Temperature and frequency dependences of relative dielectric permittivity maximum conforms the transformation from normal ferroelectric to relaxor ferroelectric behaviour. Frequency dependence of the relative dielectric permittivity maximum temperature observed for the samples with x ≥ 1.0 and satisfied the Vogel–Fulcher law. The diffuseness exponent γ (1.27–1.95) estimated from the high temperature slopes of the diffused dielectric permittivity data reveals that the degree of relaxor behavior increases with increasing the amount of Dy2O3. The temperature dependence of AC-conductivity σAC (T) analysis in the range 310 K < T < 470 K reveals the existence of variable range hopping of charge carriers with average hopping length RH and hopping energy EH are in the range 8.5–27 Å and 48–153 meV, respectively. Voltage dependent dielectric constant measurements confirm the ferroelectric nature of KNN+ x wt% Dy2O3 ceramics.

AC and DC Conductivity Studies on Lead-Free Ceramics: Sr1–xCaxBi4Ti4O15(x = 0, 0.2, 0.4, 0.6, 0.8)

Sr1–xCaxBi4Ti4O15 [x = 0, 0.2, 0.4, 0.6, 0.8] ceramics are synthesized by solid-state reactive technique. Structural analyses are done by x-ray diffraction data. Morphological studies were carried out by scanning electron microscope, and the data showed plate-like structures. To understand the conductivity mechanism, frequency and temperature dependency of AC and DC conductivity studies are carried out. The conductivity measurements are done using an impedance analyzer (Wayn–Kerr) in the temperature range 100–600°C. The frequency-dependent AC conductivity at different temperatures indicates that the conduction process follows the universal power law, and the hopping frequency shifts toward higher frequency side with increase in temperature, below which the conductivity is frequency independent. The variation of DC conductivity confirms that the ceramics exhibit negative temperature coefficient of resistance behavior at high temperature. DC conductivity values do not show any linearity with doping concentration; for a particular composition SCBT06, the DC conductivity was low.

Synthesis, Growth, and Characterization of Bisglycine Hydrobromide Single Crystal

Single crystals of BGHB were grown by slow evaporation technique. The unit cell dimensions and space group of the grown crystals were confirmed by single crystal X-ray diffraction. The modes of vibration of the molecules and the presence of functional groups were identified using FTIR technique. The microhardness study shows that the Vickers hardness number of the crystal increases with the increase in applied load. The optical properties of the crystals were determined using UV-Visible spectroscopy. The thermal properties of the grown crystal were also determined. The refractive index was determined as 1.396 using Brewster’s angle method. The emission of green light on passing the Nd: YAG laser light confirmed the second harmonic generation property of the crystals and the SHG efficiency of the crystals was found to be higher than that of KDP. The dielectric constant and dielectric loss measurements were carried out for different temperatures and frequencies. The ac conductivity study of the crystals was also discussed. The photoconductivity studies confirm that the grown crystal has negative photoconductivity nature. The etching studies were carried out to study the formation of etch pits.

Enhanced AC conductivity and dielectric relaxation properties of polypyrrole nanoparticles irradiated with Ni12+ swift heavy ions

In this paper, we report the 160MeV Ni12+ swift heavy ions (SHIs) irradiation effects on AC conductivity and dielectric relaxation properties of polypyrrole (PPy) nanoparticles in the frequency range of 42Hz–5MHz. Four ion fluences of 5×1010, 1×1011, 5×1011 and 1×1012ions/cm2 have been used for the irradiation purpose. Transport properties in the pristine and irradiated PPy nanoparticles have been investigated with permittivity and modulus formalisms to study the polarization effects and conductivity relaxation. With increasing ion fluence, the relaxation peak in imaginary modulus (M″) plots shifts toward high frequency suggesting long range motion of the charge carriers. The AC conductivity studies suggest correlated barrier hopping as the dominant transport mechanism. The hopping distance (Rω) of the charge carriers decreases with increasing the ion fluence. Binding energy (Wm) calculations depict that polarons are the dominant charge carriers.

Enhancement in electrochemical properties of ionic liquid-based nanocomposite polymer electrolytes by 100 MeV Si9+ swift heavy ion irradiation

Swift heavy ion (SHI) irradiation has been used as a tool to enhance the electrochemical properties of ionic liquid-based nanocomposite polymer electrolytes dispersed with dedoped polyaniline (PAni) nanorods; 100 MeV Si9+ ions with four different fluences of 5 × 1010, 1 × 1011, 5 × 1011, and 1 × 1012 ions cm−2 have been used as SHI. XRD results depict that with increasing ion fluence, crystallinity decreases due to chain scission up to fluence of 5 × 1011 ions cm−2, and at higher fluence, crystallinity increases due to cross-linking of polymer chains. Ionic conductivity, electrochemical stability, and dielectric properties are enhanced with increasing ion fluence attaining maximum value at the fluence of 5 × 1011 ions cm−2 and subsequently decrease. Optimum ionic conductivity of 1.5 × 10−2 S cm−1 and electrochemical stability up to 6.3 V have been obtained at the fluence of 5 × 1011 ions cm−2. Ac conductivity studies show that ion conduction takes place through hopping of ions from one coordination site to the other. On SHI irradiation, amorphicity of the polymer matrix increases resulting in increased segmental motion which facilitates ion hopping leading to an increase in ionic conductivity. Thermogravimetric analysis (TGA) measurements show that SHI-irradiated nanocomposite polymer electrolytes are thermally stable up to 240–260 °C.

WITHDRAWN: Impedance and ac conductivity studies on highly resistive BiFeO3 nanoceramics

WITHDRAWN: Impedance and ac conductivity studies on highly resistive BiFeO3 nanoceramics

AC conductivity and dielectric studies of modified Li4SiO4 ceramic electrolytes

AC conductivity of modified Li4SiO4 (Li3.94Cr0.02SiO4, Li4Zr0.06Si0.94O4 and Li3.94Cr0.02Zr0.06Si0.94O4) was measured as a function of frequency in the range between 1Hz to 1000Hz and in temperature range between 303K to 773K. The frequency dependence of conductivity for these ceramic electrolytes followed the universal power law variation, σAC (ω)=σo+Aωs. The plots of pre-exponent s versus temperature of all systems suggested that the conduction mechanism in all systems can be described using correlated barrier hopping model. Meanwhile, the charge carrier concentration and mobile ion concentration in all samples was found to be constant over the temperature range of this study while mobility of ion increased with temperature implying that the increase in conductivity with temperature was due to the increase in ion mobility. The experimental results also revealed that the dielectric constant and dielectric loss decreased with frequency. The double substituted sample, Li3.94Cr0.02Zr0.06Si0.94O4 showed the highest dielectric constant and dielectric loss at low frequencies. The increase in temperature also increased the dielectric constant and dielectric loss values in all samples.

Structural, morphological and ac conductivity study of PrFe0.5Ni0.5O3 thin film

Thin film of PrFe0.5Ni0.5O3 was synthesis by pulsed laser deposition technique on silicon wafer. The structure and phase identification of the film was carried out by X-ray diffraction and confirms orthorhombic structure with polycrystalline growth. Atomic Force Microscopy (surface morphology) shows small grain size with good smoothness for the grown film. From dielectric study, low dielectric loss and week ferroelectric nature is observed at room temperature. Various possibilities were explored to explain the observed dielectric properties with the proposed crystal structure.

Impedance spectroscopic analysis of the organic ferroelectric – Diisopropylammonium bromide (DIPAB)

We report the dielectric and ac conductivity studies on the organic molecular ferroelectric, diisopropylammonium bromide polycrystalline sample. The frequency and temperature dependant real and imaginary parts of the impedance show two relaxations in the sample. The Nyquist plots exhibit two semicircles revealing both grain and grain boundary contributions to the resistance above Curie temperature. We find that the compound shows a non-Debye type relaxation behavior and the conductivity follows the semiconducting behavior. The conduction mechanism can be explained by the barrier hopping model.

Structural, dielectric and impedance spectroscopy studies in (Bi0.90R0.10)Fe0.95Sc0.05O3 [R=La, Nd] ceramics

Polycrystalline BiFeO3 and (Bi0.90R0.10)Fe0.95Sc0.05O3 [R=La, Nd] ceramics were synthesized by solid-state reaction method. XRD studies confirmed the formation of single-phase compositions. The particle sizes obtained from XRD data were 43, 31 and 30nm for BFO, BLFSO and BNFSO, respectively. Dielectric studies revealed anomalies around 200°C and near the Néel temperature. The latter is attributed to the phase transition as an influence of vanishing magnetic order on the electric order usually observed in magneto-electric ordered systems. Complex impedance spectroscopy (CIS) technique was utilized to investigate the intra- and inter-granular contributions to the impedance in the studied compositions as a function of temperature and frequency. CIS studies revealed that the electrical relaxation process was temperature dependent and non-Debye type. AC conductivity studies revealed that conductivity in samples was mainly due to the hopping of oxygen vacancy between the oxidation states (Fe3+/Fe2+) of iron.

Structural, dielectric, ferromagnetic, ferroelectric and ac conductivity studies of the BaTiO3–CoFe1.8Zn0.2O4 multiferroic particulate composites

Multiferroic particulate composites comprising BaTiO3 as ferroelectric phase and CoFe1.8Zn0.2O4 as ferrite phase with the formula (1−x) BaTiO3–(x) CoFe1.8Zn0.2O4 (where x=10, 20, 30 and 40wt%) are fabricated by the solid state reaction method. To check the phase purity and structure formation, X-ray diffraction (XRD) technique has been used. XRD patterns confirm the formation of the individual phases and the composites. Using scanning electron microscopy (SEM), the morphology of the composites is studied and reveals an increase in grain size with ferrite content. In addition, significant effect of ferrite content on the dielectric, electric and magnetic properties of the composites has also been observed. Variation of dielectric constant (ε׳) and loss tangent (tan δ) with temperature (up to 400°C) and frequency (20Hz–1MHz) have been investigated. Dielectric constant is found to increase as ferrite fraction increases with the appearance of two peaks, one in the lower temperature region and other in the higher temperature region. Peak observed in the low temperature range (120°C–150°C) is ascribed to ferroelectric to paraelectric phase transition of the BaTiO3 phase. The increase in dielectric constant can be attributed to the space charge effect and the hopping conduction mechanism. Besides this, the variation of loss tangent (tan δ) with temperature of the composites exhibits loss peaks. With increasing frequency, all the composites show usual dielectric dispersion. AC conductivity of the composites has been studied as a function of frequency and temperature to understand the conduction mechanism. The observed behavior of the conductivity can be interpreted using a jump relaxation model (JRM). Polarization (P) vs. Electric field (E) and Magnetization(M) vs. Magnetic field (H) loops are measured at room temperature which demonstrates that all the composites exhibit simultaneously good ferroelectric and ferromagnetic properties.

Optical, electrical properties, characterization and synthesis of Ca2Co2O5 by sucrose assisted sol gel combustion method

Sol–gel combustion method has been used as an efficient and simple method to synthesize pure Ca2Co2O5 (CCO-225) ceramic powder using sucrose which play a dual role as the gelling agent and combustion fuel. The advantage of this method is simple low cost and environmental friendly. The synthesized sample is sintered at various temperatures the products were characterized by powder X-ray diffraction (XRD), Thermogravimetric and differential thermal analysis (TGA-DTA), Fourier transformer infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and UV–Visible diffuse reflectance spectroscopy (DRS). X-ray diffraction pattern of sintered sample at 800°C confirmed the formation of single phase Ca2Co2O5 and also it is proved in thermal analysis. SEM image indicates the obtained samples are diffused platelet like morphology and its grain size will be in the range of 150–300nm. CCO-225 ceramic material has a wide range of optical and electronic applications due to its wide band gap energy of 3.50eV. The dielectric constant, dielectric loss and AC conductivity were analyzed at different temperatures and frequencies of the applied field. The AC conductivity studies carried out in the frequency range of 50Hz to 5MHz at various temperatures from 30°C to 400°C. The result reveals that the space charge polarization leads for conduction mechanism.

Ac conductivity and dielectric spectroscopy studies on tin oxide thin films formed by spray deposition technique

Au/tin oxide/n-Si (100) structure has been created by forming a tin oxide (SnO2) on n-type Si by using the spray deposition technique. The ac electrical conductivity (σac) and dielectric properties of the structure have been investigated between 30kHz and 1MHz at room temperature. The values of ε', ε″, tanδ, σac, M' and M″ were determined as 1.404, 0.357, 0.253, 1.99×10−7S/cm, 0.665 and 0.168 for 1MHz and 6.377, 6.411, 1.005, 1.07×10−7S/cm, 0.077 and 0.078 for 30kHz at zero bias, respectively. These changes were attributed to variation of the charge carriers from the interface traps located between semiconductor and metal in the band gap. It is concluded that the values of the ε', ε″ and tanδ increase with decreasing frequency while a decrease is seen in σac and the real (M') and imaginary (M″) components of the electrical modulus. The M″ parameter of the structure has a relaxation peak as a function of frequency for each examined voltage. The relaxation time of M″(τM″) varies from 0.053ns to 0.018ns with increasing voltage. The variation of Cole–Cole plots of the sample shows that there is one relaxation.

Dielectric and Ac Conductivity Studies of Mn-Doped Na1.86Li0.10K0.04Ti3O7Ceramics

Dielectric-spectroscopic and ac conductivity studies on 0.01 and 1.0 molar percentage manganese doped layered Na1.86Li0.10K0.04Ti3O7 ceramics have been reported. The dependence of loss tangent (tan δ) and relative permittivity (er) on temperature in the range 350 775 K and on frequency in the range 10 kHz 1 MHz have been undertaken. The losses are the characteristics of dipole mechanism, electrical conduction and space charge polarization. The obtained conductivity plots between log(σacT ) versus 1000/T have been divided into four regions namely region I, II, III, and IV. The mechanism of conduction in region I is acknowledged to electronic hopping conduction. The less frequency and more temperature dependent region II is ascribed as a mixed mechanism associated interlayer ionic conduction, electron hopping, and alkali ion hopping conduction . The unassociated interlayer ionic conduction along with alkali ion hopping conduction mechanisms are contributing to the transport process in the mid temperature region III. The mechanism of conduction in the highest temperature region IV may be recognized as the modi ed interlayer ionic conduction. The conductivity versus frequency curves lead to conclude that the electronic hopping conduction diminishes with the rise of temperature.

Electrical Conductivity Studies Of Pani-Flyash Blends

The conducting polymers have conjugated double bonds in their backbone.There are many different types of conducting polymers. The most common conducting polymers are Polyacetylene (PA),Poly (phenylene), Polythiophene Polypyrrole,Polyaniline(PANI) etc., . The addition of FLYASH in PANI results in an enhancement of microwave absorption with an added advantage of industrial waste utilization. The PANI-FA compositeswere prepared with different concentration of flyash to aniline ratio (50:50,60:40,70:30,80:20).AC and DC conductivity studies were carried out for the blends using Four probe technique for various temperature.

Dielectric properties and signature of multi-ferroelectricity in Co2FeO4: A structurally single phased and bi-phased spinel oxide

The ferrite Co2FeO4 has been stabilized in single phased and bi-phased cubic spinel structure depending on annealing temperature of as prepared sample. This ferrite showed many interesting dielectric properties. AC conductivity study showed semiconductor characters with activation energy in the range 0.46–1.02eV. The combination of small and correlated barrier hopping of polarons controlled AC conductivity mechanism in the samples. Cole–Cole plot of the complex impedance spectrum suggested dielectric contribution from grains and grain boundaries of the material and electrical modulus confirmed it. The present ferrite material shows sufficiently large dielectric constant (30–200) and remarkably low loss (0–0.35) in a wide range of temperature and frequency. The single phased sample has shown lowest conductivity and dielectric loss. Maxwell–Wagner type interfacial polarization affected the dielectric properties at lower frequencies. A broad bump/peak in the temperature dependence of dielectric constant curves signalled the multi-ferroelectric nature of the material. Room temperature ferroelectric loop is, indeed, good in some of the samples and magnetic field controlled ferromagnetic blocking has been tailored in a wide temperature range 80–400K.

Structural, FTIR and ac conductivity studies of NaMeO3(Me ≡ Nb, Ta) ceramics

Lead-free complex perovskite ceramics NaMeO3 (Me = Nb, Ta) were synthesized using conventional solid state reaction technique and characterized by structural, FTIR and electrical (dielectric and ac conductivity) studies. The crystal symmetry, space group and unit cell dimensions were determined from the experimental results using FullProf software. XRD analysis of the compound indicated the formation of single-phase orthorhombic structure with the space group Pmmm (47). Dielectric studies showed the diffuse phase transition at 394C for NaNbO3 and 430C for NaTaO3. Ac conductivity in both the compounds follows Jonscher‟s power law.

Electrical and dielectric properties of nanocrystalline LaCrO3

The X-ray diffraction pattern of nanocrystalline LaCrO3 synthesized by combustion method reveals the perovskite phase of the material. The synthesized material has an average crystallite size of 24 nm. The characterization techniques such as X-ray diffraction studies, scanning electron microscopy, transmission electron microscopy etc., were employed to study the average particle size, phase and composition of the material. The effects of constituent phase variation on the dielectric, resistivity and impedance properties are examined. The dielectric dispersion with frequency has been explained on the basis of an electron–hole hopping mechanism, this is responsible for conduction and polarization. From the ac conductivity study, it is confirmed that the conduction in the present material is of small polaron type. Such materials may be useful to fabricate the interconnecting materials for the solar cell, gas sensors, gas transducers, optoelectronic devices, catalyst etc.

Structural, dielectric and electrical studies of MgAl2−2xY2xO4 (x = 0.00–0.05) cubic spinel nano aluminate

Investigations were carried out on a series of MgAl2-2xY2xO4 (x = 0.00–0.05) nanoparticles prepared in steps of 0.01 by chemical co-precipitation method to study the effect of yttrium substitution at aluminum site on the structural, dielectirc and electrical properties. The single phase cubic spinel structure of all the samples was confirmed by X-ray diffraction (XRD). The Fourier transform infrared spectroscopy (FTIR) study shows two strong absorption bands in the frequency range 400–800 cm−1, on the tetrahedral and octahedral sites respectively. Elemental analysis by Energy dispersive X-ray fluorescence (EDXRF) shows that samples are stoichiometric. The scanning electron microscopy (SEM) study reveals surface morphology of nanoparticles. Transmission electron microscopy (TEM) study shows the individual nanoparticles size and validates the nanocrystalline nature of the samples. The variation of dielectric permittivity at room temperature as a function of frequency (1 KHz to 1 MHz) suggests the dielectric dispersion due to Maxwell-Wagner Interfacial Polarization. AC conductivity study reveals that the conduction is due to small polaron hopping. The electrical modulus analysis shows that nanocrystalline MgAl2−2xY2xO4 system exhibits non Debye type relaxation. The dc resistivity was found to increase with increase in yttrium content.

Relaxation process in PbI2–Ag2O–V2O5–B2O3 system: Dielectric, AC conductivity and modulus studies

Abstract Silver ion conducting super-ionic glass system xPbI2–(100 − x) [Ag2O–2(V2O5–B2O3)], where, 5 ≤ x ≤ 25, were prepared via melt quenching route and -characterized by XRD and DSC. Their electrical properties were measured by impedance spectroscopy in the frequency range of 2 MHz to 20 Hz from 30 to 120 °C. The electrical relaxation mechanism has been studied using AC conductivity, dielectric modulus function and frequency dependent dielectric permittivity over a wide range of frequency and temperature. Two different scaling approaches for AC conductivity as well as dielectric permittivity spectra were used to understand the nature of relaxation processes.